To better understand the molecular basis of epidermal differentiation, and the structure and development of the integument generally, we study a variety of skin disorders to determine the underlying genetic error. This leads to hypotheses about the function of the causative gene in health and disease. Specific hereditary disorders are selected for study, and affected and unaffected members of many families evaluated clinically. A phenotypically homogeneous set of families is defined after careful clinical study. Gene localization methods (linkage analysis using candidate loci and/genome screening techniques) are used to identify the causative locus. Genomic organization is defined and a wide variety of mutation detection assays are used to define the spectrum of mutations in the disease. Goals include correlation of the molecular findings with the clinical presentation of the disorder to better understand the structure/function relationship of the gene expression in human tissues, and collaboration with cell biology and other laboratories with a mechanistic interest to determine the cellular sequelae of the gene mutation.In the past year we have been developing several new automated methods for identifying mutations in the PTCH gene (the human homolog of Drosophila patched) in our series of patients with Gorlin syndrome and in a series of patients ascertained because of the presence of odontogenic keratocysts. These new methods now allow molecular diagnosis in a clinical setting in our now-CLIA 88 approved laboratory. We have developed a rapid assay based on cDNA screening for characterizing mutations in TGM1, the gene we recently as causing the severe autosomal recessive disorder, lamellar ichthyosis. This method has facilitated the identification of a common splice-site mutation, thought primarily to occur in Norwegians, in patients from various non-Norwegian backgrounds. Detailed haplotype analyses in these patients suggest that the splice site mutation arose on a German background. It was likely was introduced into Norway around 800-1000 AD and spread through that population due to a founder effect.We are continuing our analysis of families with ichthyosis vulgaris. In one large family, a histologic variable appears to co- segregate with genetic markers on chromosome 1q.Two other families with clinical ichthyosis vulgaris but without the histologic variable have been ascertained and linkage studies are being performed. A musculoskeletal disorder, autosomal recessive Kuskokwim syndrome, has been under study. We selected this disorder to test a method of DNA pooling in the laboratory. A complete genome screen using pooled DNA samples from 15 families and controls has been completed, and the chromosomal location of the KS gene has been This congenital arthrogyposis is found only in the Yupik Eskimos, and our results will now allow for carrier detection based on our identification of a carrier-associated haplotype in the population. Fine-mapping of candidate genes in the region using radation hybrids is underway. We have screened two candidate genes in the region for mutations, and excluded both candidates.We have ascertained several families, including 11 affected individuals, with Hermansky-Pudlak Syndrome from central Puerto Rico. These patients do not have the 16bp duplication found in the HPS1 gene in Northwest Puerto Rican patients, nor do they have any other mutation in the HPS1 gene. We are using DNA pooling analysis to identify the chromosomal region of the gene for this Hermansky-Pudlak variant.The approach we have chosen, detailed clinical and laboratory investigation of rare hereditary disorders, has been very fruitful in elucidating knowledge about the structure, function, and differentiation of the skin and related organ systems. - Genetics, skin, ichthyosis, Gorlin syndrome, mutation detection, musculoskeletal disease, linkage analysis - Human Subjects & Human Subjects: Interview, Questionaires, or Surveys Only